Simultaneous conversion and fusion of electrostatically producer printing masters

ABSTRACT

TO PROVIDE A PRINTING MASTER, BY THE ELECTROSTATIC PROCESS, A MASTER SHEET IS CHARGED AND SELECTIVELY DISCHARGED AND THEN TONED IN THE CONVENTIONAL MANNER TO PRODUCE AN IMAGE. THE TONED MASTER IS THEN BROUGHT INTO CONTACT WITH A HEATED CONVERSION SOLUTION TO SIMULTANEOUSLY FIX THE IMAGE AND CONVERT THE MASTER NON-IMAGE AREAS FROM A HYDROPHILIC CONDITION.

United States Patent Office 3,701 ,673 Patented Oct. 31, 1972SIIVIULTANEOUS CONVERSION AND FUSION OF ELECTROSTATICALLY PRODUCERPRINTING MASTERS Martin W. Hellar, Novelty, and Michael A. Kiener,Cleveland, Ohio, assignors to Addressograph-Multigraph Corporation,Cleveland, Ohio No Drawing. Filed Jan. 20, 1971, Ser. No. 108,214 Int.Cl. G03g 13/06 US. Cl. 117-175 2 Claims ABSTRACT OF THE DISCLOSUREBACKGROUND OF THE INVENTION This invention relates to the production ofplanographic printing masters. Photoconductors are used to arrange tonermaterial on a sheet in the image of an original subject. Then, it isusually necessary to treat such a master to make the backgroundhydrophilic. This invention is useful in all such systems, but findsparticular application in an electrostatically produced master of thetype having a surface coating of a photoconductor normally oleophilic,which must then be chemically reacted to establish a hydrophiliccondition. Hence, the preferred embodiment of the invention will bedescribed in its application to an electrostatic master.

One method of producing a lithographic printing master is by theelectrostatic process. In this process, a master sheet coated with aphotoconductive material is charged, then exposed to dissipate thecharge in the non-image areas, to provide the desired latent imagethereon. A toner is then applied to the surface, which toner will adhereto the charged surface where the latent image is formed. Such toner,when held on the surface only by electrostatic charge, is easilyremoved. According to conventional prior art practice, therefore, thistoner is then fixed at elevated temperatures, i.e. the toner is heatedto such a degree that it firmly adheres to the paper which thus sets thetoner on the surface. This fixing has conventionally been done with highwattage lamps, utilized to generate radiant energy, or by ovens.

Once the toner has been fixed, the entire surface of the master is thentreated with a conversion solution. The conversion solution chemicallyconverts the non-image areas, i.e. the background photoconductivematerial, to a water insoluble hydrophilic material. The fixed toner, inthe form of the image, is and remains oleophilic. Thus, the master willreceive ink in the image area and reject it in the background. All ofthis in well known in the art.

One of the disadvantages to the above described prior art process, isthe large number of separate steps which must be performed. Each ofthese separate steps require a separate processing station andassociated equipment in the devices designed for producing the masters.

Another drawback to the above entitled process, is the need for highwattage heat elements. Not only do these elements require a large powerinput, they also present a potential fire hazard because of the heatgenerated.

Another deficiency or drawback in the above described process, is thesomewhat limited number of conversion soluitons which can be utilized atambient temperatures, since many potentially useful conversion solutionsreact at rates so slow as to be commercially or convenientlyunacceptable. This has necessitated utilizing relatively unstablesolutions to achieve the necessary rate of conver- S1011.

SUMMARY OF THE INVENTION According to the present invention, a masterhas the latent image formed thereon in the conventional manner. andtoner applied in a conventional manner. A conversion solution ismaintained at, or above, the temperature. required to fix the toner. Themaster is contacted by the solution for a sufficient period of time tosimultaneously fix the toner and convert the background.

DESCRIPTION OF THE PREFERRED EMBODIMENT The process of the presentinvention, as described in the summary above, contemplates thesimultaneous background conversion, and fixing of an image ofconventionally produced electrostatic master to convert the master to asuitable condition for lithographic printing.

In the practice of the present invention, any master. sheet havingphotoconductive material which can be converted to a water insolublehydrophilic material can be utilized. Examples of such potentialmaterials include metal oxides and sulphides. Of these, zinc oxide is byfar the most commonly used material and hence is preferred for thisinvention.

The coated master is first given a uniform surface charge, and thenselectively discharged by exposure to a pattern of light and shadow. Thelight struck area will discharge, leaving a charged area latent imagethereon in the desired shape to be printed. Toner is then applied whichwill adhere to the charged latent image. There are various formulationsof toners which can be utilized. Basically, all

of thees toners are natural or synthetic resins, or mixtures of resins,and have carbon black and/or dyes. The temperature required to fix thesetoners varies, and is determined by their composition. The preferredtoner is a mixture of natural and synthetic resins with suitable dyes,and carbon black. This toner must be heated to approximately C., orabove, to obtain the required degree of fixing. When the toner is heatedto or above this temperature, it will firmly adhere to the sheet,forming a relatively permanent image configuration thereon. This issometimes referred to as fusing the toner, although it is doubtful thatcomplete or even any appreciable melting is required to obtainsatisfactory adherence to the sheet. This toner is oleophilic and willaccept grease ink for printing.

The above steps are all conventional prior art practice.

When the toner has been applied, the master is then brought into contactwith a conversion solution heated to a temperature above the temperaturerequired to fix the toner. Usually, with most conventional toners, thesolution must be heated to at least 80 C. While there are many solutionsor compounds which are suitable for converting the zinc oxide to ahydrophilic-oleophobic form, such as oxalates, citrates, and tartrates,the preferred solution of 10% mono-ammonium phosphate, with 5% glycerin,and 0.03% sorbic acid added thereto. The phosphate is the convertingagent, the glycerin is a humectant and wetting agent, and the sorbicacid a mold inhibitor. This solution is quite stable at temperatures of80 C. and above, and has a virtually indefinite shelf life. Otherphosphates, such as monosodium phosphate, are also well adapted forconversion purposes.

The imaged and toned master is maintained in contact with the liquidsolution at the elevated temperature a sufficient period of time to fixthe image and convert the background to a water insoluble hydrophilicmaterial. The fixing process, with most toners, is a time-temperaturedependent relationship; the, higher the temperature, the less timerequired. to complete the fixing process. The upperlimit for thetemperature is controlled only by the characteristics of the conversionsolution and the material of the components of the master; i.e. thetemperature cannot be too high to degrade or impair the conversion reaction or to degrade any of the components of the master or solution. Withaqueous solutions, the upper limit'is therefore,-about 100 C., theboiling point of water. However, it is normally desirable to operate atthe minimum temperature which will give sufficiently rapid conversion,and effective fixing since this will minimize power requirements. In thepreferred embodiment, temperatures of 81 to 84 C. are satisfactory, andadequate fixing is completed within about 0.3 second. Conversion is alsocompletewithin this same time, andthe master is then ready for printing.

Thus, according to this invention, the fixing of the toner andconverting of the background is accomplished in a single step, ratherthan in two steps, therebyeliminating one processing step. Also, theenergy requirements to maintain the solution in the 81 to 84 C. range,are substantially less than the energy requirement to operate the heatlamps or ovens in the prior art devices. Further, the elimination of theheat lamp or ovens eliminates potential fire hazards.

Another benefit of the present process, is that phosphate conversionsolutions are commercially practicable. These solutions are desirablesince they are stable and have virtually indefinite shelf life. However,when phosphate solutions are used at ambient temperatures, i.e. about 20C., the rate of the conversion reaction is so slow that they are notconvenient in a machine copier. Hence, other converting agents, such asferrocyanides have been used since they react rapidly enough at ambienttemperatures. However, these agents are comparatively unstable, with aresulting short shelf life. Thus, by operating at temperatures of 80 C.,and above, the rate of the conversion reaction of the phosphates withthe zinc oxide is sufiiciently rapid to be commercial, therebypermitting their use and, hence, avoiding the undesirablecharacteristics of the ferrocyanide solutions.

What is claimed is:

1. In the process of forming a printing master wherein an electrostaticimage is formed by selectively charging the surface of a master sheethaving a photoconductive material thereon to form a latent image, andapplying a toner to develop the image and wherein the toner must befixed and the non-imaged areas converted to water insoluble hydrophilicmaterial;

the improvement which comprises, providing a conversion liquid whichwill convert the non-imaged material at a temperature above thatrequired to fix the toner, and contacting the surface having the unfixedtoner thereon with said liquid at a temperature at least as high'as thetemperature required to fix said toner and lower than that which woulddegrade any of the components of the master and liquid for a suflicienttime to fix the toner and convert the non-imaged areas, whereby tosimultaneously convert the background and fix the image. 2. Theinvention as defined in claim 1 wherein the liquid is an aqueoussolution.

References Cited UNITED STATES PATENTS 3,001,872 9/1961 Hurz l0l4633,107,169 10/1963 Bornarth 101-466 3,278,323 10/1966 Kalman et a1.1l7-17.5 3,567,484 3/1971 White et a1 117-21 WILLIAM D. MARTIN, PrimaryExaminer M. SOFOCLEOUS, Assistant Examiner US. Cl. X.R.

